Temperature limitations for IR extrinsic and intrinsic photodetectors

The temperature limitations for IR extrinsic and intrinsic photodetectors axe theoretically studied by comparing the detectivity limitations. This comparison indicates that the temperature superiority of the intrinsic detector is identified with the inequality
B_{E}/\sigma_{E} > B_{I}/(\alpha_{I}/\sqrt{N_{C}N_{V}})
where B
E
, B
I
are the respective recombination coefficients of the extrinsic and intrinsic detectors and σ
E
and
\alpha_{I}/\sqrt{N_{C}N_{V}})
are the respective optical absorption cross sections. The highest operational temperature for a given background radiation level for each species is established when the recombination coefficients are radiative limited. For the same spectral cutoff wavelength, refractive index and quantum efficiency, they will then have identical operational temperatures. Comparison with experiment shows that the intrinsic detectors achieve a closer approach (because of the inequality) to the theoretical limit than do the extrinsics. The prospects for achieving a closer approach to this limit with the extrinsics are discussed.